Molecular genetics exam 3 Flashcards
(165 cards)
1
Q
Mendel chose the garden pea as his model system because
A
obvious phenotypes, easy to control pollination, short generation time, and a lot of progeny
2
Q
Name 5 characteristics that are important for a good model organism
A
easy to breed, easy to maintain, a lot of progeny, observable characteristics, and true breeding strains
3
Q
name the 7 characteristics that Mendel observed
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seed color, seed shape, seed coat color, pod color, pod shape, flower position, and stem length
4
Q
Gene
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an inherited factor(region of DNA) that helps determine a characteristic
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Q
Allele
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One of two or more alternative forms of a gene
6
Q
Locus
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Specific place on a chromosome occupied by an allele
7
Q
Genotype
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Set of alleles possessed by an individual organism
8
Q
Heterozygote
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an individual organism possessing 2 different alleles at a locus
9
Q
Homozygote
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an individual organism possessing 2 of the same alleles at a locus
10
Q
Phenotype of a trait
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appearance or manifestation of a characteristic
11
Q
characteristic or character
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an attribute or feature possessed by an organism
12
Q
Genotype is the listing
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of alleles an individual carries for a specific gene
13
Q
WW is
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Homozygous dominant
14
Q
Ww is
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heterozygous
15
Q
ww is
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homozygous recessive
16
Q
The molecular difference between alleles can be detected as a restriction length polymorphism (RFLP) using
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the enzyme EcoRl and a probe that hybridizes at the site shown
17
Q
P generation (P1 or P0) is
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the initial cross
18
Q
True breeding
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have the same alleles for the gene
19
Q
With true breeding strains, every time you self breed them you get
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100% of the population as with the same phenotype as parent
20
Q
If you breed 2 pure lines then the F1 is
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heterozygous and displays the dominant phenotype
21
Q
a cross of F1 plants forms the
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f2 generation
22
Q
2 heterozygotes crossed leads to what ratio of genotypes
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1:2:1
1 YY, 1 Yy and 1 yy
23
Q
2 heterozygotes crossed leads to what ratio of phenotypes
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3:1
24
Q
Results can be expressed as
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homozygous or heterozygous
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monohybrid crosses involve __ gene(s)
1
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Monohybrid crosses reveal how
one trait is transmitted for generation to generation
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Name of mendels 3 postulates
unit factors in pairs, dominance/recessiveness, and segregation
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Describe the unit factors in pairs postulate
genetic characters are controlled by unit factors (genes) existing in pairs in individual organisms
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Describe dominance/recessiveness postulate
In the pair of unit factors for a single characteristic in an individual, one unit factor is dominant and the other is recessive
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Describe segregation postulate
the paired unit factors segregate (separate) independently during gamete formation
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A way to determine whether an individual displaying the dominant phenotype is homozygous or heterozygous for the trait is to
test cross with a ww homozygous recessive because if it it is homozygous dominant, all of the progeny will be dominant because the dominant allele will hide it
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what does not true breeding mean??
heterozygous for the trait
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dihybrid cross involves
2 independent traits
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what is mendels fourth postulate
independent assortment-traits assort independently during gamete formation and all possible combinations of gametes will form with equal frequency
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the principle of segregation says that the alleles____ and the principle of independent assortment says that alleles ____
separate, separate independently of alleles at different loci
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Trihybrid cross
involves 3 independent traits
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chromatin fibers coil and condense to form __ during mitosis and meiosis
chromosomes
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Chromosomes exist in __ in diploid organisms
homologous pairs
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Somatic cells are aka
body cells
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Humans have 46 chromosomes or 23__
pairs
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how many autosome pairs are there?
22
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how many pairs of sex chromosomes are there
1
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Homologous chromosomes carry genes for
the same inherited characteristics but are not identical
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what are alleles
different versions of the same genes
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Genetic locus
the location of a particular gene on a chromosome
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at each genetic locus, an individual has __ alleles, or one on each chromosome
2
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are sex determining chromosomes homologous?
usually not homologous yet behave as homologous in meiosis
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what does the letter before n mean ex. 2n
number of sets (2 sets)
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n means
the number of unique chromosomes
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chromatid is an
unreplicated chromosome
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after replication there are 2 chromatids connected by a
centromere
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what are the 2 chromatids connected by a centromere that are exactly the same?
sister chromatids
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what are non sister chromatids?
a chromatid from each chromosome from a pair of homologous chromosomes
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homologous chromosomes carry the same genes but can carry different __ of those genes
alleles
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In males, how may of the 4 products of meiosis develop into functional sperm?
4
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In females, how many of the 4 products of meiosis develop into an egg?
1
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the egg producing spore in higher plants is the
megaspore
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the sperm producing spore in higher plants is the
microspore
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in higher plants, the diploid spore producing generation (___) is conspicuois
sporophyte
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in higher p-lants, the gamete producing (___) generation is microscopic
gametophyte
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meiosis creates __ and mitosis creates the __
gametes, organism
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what is meiosis
specialize form of cell division that makes sexual reproduction possible and produces gametes or sex cells
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why does meiosis reduce the genetic info passed down to the daughter by half?
sperm and egg come together to make 2n a diploid organism
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why do males create 4 sperm to a females 1 egg?
the egg provides every component of the cell and thus there is an unequal division of the cytoplasmic material and sperm only contributes DNA
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in mitosis the daughter cells are _n
2
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in meiosis the daughter cells are _n
1
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when does crossing over occur?
In prophase 1
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when do homologous pairs of chromosomes allign on the metaphase plate?
metaphase 1
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when do pairs of chromosomes separate?
anaphase 1
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when do individual chromosomes allign on the metaphase plate?
metaphase 2
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when do chromatids separate?
anaphase 2
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meiosis 1
reduces the number of chromosomes by separating homologous pairs
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meiosis 2
separates sister chromatids into 2 different daughter cells
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which part of meiosis looks exactly like mitosis?
meiosis 2
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what happens in prophase 1?
homologous chromosomes pair and crossing over between non sister chromatids
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why is chromosome pairing important?
so that the number of chromosomes can be reduced
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what is crossing over?
an equal exchange of genetic material such that nothing is lost. It is a rearrangement such that alleles will be inherited will alleles of different genes
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what happens in metaphase?
paired homologas chromosomes line up together on the metaphase plate and independent assortment
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what is independent assortment
orientation of pairs to poles is random. this leaves some paternal and some maternal on the left and right
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what happens in anaphase 1
homologous chromosomes separate and move toward poles
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what happens in telophase 1?
each pole now has a haploid set of chromosomes
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the 2 cells at the end of meiosis 1 now have a compliment of
n
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meiosis 2 starts as __ and ends as __
haploid, haploid
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meiosis 1 starts as __ and ends as __
diploid, haploid
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what is the product law?
when 2 independent events occur simultaneously, the probability of the two outcomes occurring incolmbineation is equal to the product of their individual probabilities
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what does a pedigree analysis do?
demonstrates a family tree with respect to a given trait and reveals a pattern of inheritance
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the sex of the progeny after fertilization is determined by the
sex chromosome contained in the sperm
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the result of meiosis is _ type(s) of egg and __ type(s) of sperm
1, 2
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heteromorphic chromosomes (___) characterize ___
(dissimilar) one sex or the other
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what is another word for heteromorphic chromosomes
sex chromosomes
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what serves as the underlying basis of sex determination?
genes, not chromosomes
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life cycles depend on
sexual differentiation
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in multicellular organisms it is important to distinguish between __ and __
primary sexual differentiation and secondary sexual differentiation
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what is primary sexual differentiation?
involves only the gonads where gametes are produced
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what is secondary sexual differentiation ?
involves the overall appearance of the organism
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what is unisexual?
individuals that contain only male or female reproductive organs
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what are 2 other names for unisexual?
dioecious or gonochoric
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what is bisexual?
individuals that contain both male and female reproductive organs and can produce both male and female gametes
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2 other names for bisexual
monoecious and hermaphroditic
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for c elegans XX is
hemaphrodite
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for c elegans X or X0 is
male
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for c elegans, when males are crossed with a hermaphrodite, the progeny will be
50% hermaphrodite and 50% male
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Female gametes have _ chromosome(s)
x
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Male gametes have _ chromsome(s)
either an x or y
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in chromosomal sex determination, each son gets his X chromosome from his _ and y from his _
mother, father
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two X chromosomes (_) result in _ offspring
homogametous, female
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one x and one Y chromosome (_) result in _ offspring
heterogametous. male
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pseudoautosomal regions present where?
on Both ends of the y chromosome
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pseudoautosomal regions share homology with regions on the _ chromosome
x
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Y chromosomes have at least _ genes
75
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which chromosome has pseudoautosomal regions?
y chromosomes
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SRY is the
sex determining region on a y chromosome
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when do SRY genes become active in XY embryos
6-8 weeks of development
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what is the testis determining factor (TDF)?
a protein encoded by a gene in the SRY that triggers testes formation
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what is nondisjunction?
when the chromosomes do not properly segregate during meiosis
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what happens if nondisjunction occurs?
if this happens to the X chromosome, the result is 1 egg with 2xs and one with none. When it joins the sperm it can result in a number of disorders. it can also happen in sperm
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homozygous traits, if parents are unaffected Both parents must be
heterozygous
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sex determination in drosphilia
Y does not determine sex. Sex is determined by the ration of X chromosomes to autosomes
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what controls sex determination in reptiles?
temperature
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For all crocodiles, most turtles, and some lizards, sex determination is achieved according to the
incubation temperature of eggs during a critical period of embryonic development
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what is the genie sex determining system?
No sex chromosomes, only sex determining genes. Found in some plants fungi, protozoans and fish
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sex linked characteristics
gene located on the sex chromosome
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dosage compensation of x linked genes
prevents excessive expression of x linked genes in humans other than mammals and balances the dose of X chromosome gene expression in females and males
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a calico cat is female and the coloring pattern is due to
dosage compensation
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describe dosage compensation in cats
fur color is on the X chromosome so when some cells deactivate the x for black and some cells deactivate the x for orange, both will be expressed.
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what is dominant and recessive inheritance?
when it deals with recessive and dominant inheritance
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what is incomplete dominance?
The resulting offspring have a phenotype that is a blending of the parental traits.
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in incomplete dominance and codominance how do the phenotypic and genotypic ratio compare? Why?
they are the same. because heterozygotes have their own phenotype
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what is codominance?
two alleles at a locus produce different and detectable gene products in heterozygote. A condition in which both alleles for a gene are fully expressed
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what occurs due to codominance?
No dominance or recessiveness, no blended phenotype
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multiple alleles
three or more alleles of a gene that code for a single trait
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Blood type a or Ia allele is responsible for
an enzyme that can add the terminal sugar n-acetylflactosamine to the H substance
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Blood type B or Ib is responsible for
a modified enzyme that can add a terminal galactose
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Blood type or or the o phenotype results
from an absence of either terminal sugar
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Ia and Ib alleles
are dominant over I
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Ia and Ib alleles are
codominant
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Type 0 blood type has what kind of antigens? antibodies?
none, anti a and anti b
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type a has what kind of antigens?antibodies?
a, anti b
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type b has what kind of antigens? antibodies?
b, anti a
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type ab has what kind of antigens? antibodies?
a and b, none
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what is an example of multiple alleles?
colors of rabbits
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what is pleiotropy?
when the expression of a single gene has multiple phenotypic effects
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give an example of pleiotropy
marfan syndrome-the autosomal dominant mutation in the gene encoding the connective tissue protein fibrillar
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what all does Marfan syndrome cause?
Many tissues including eye lens dislocation, increased risk or aortic aneurysm and lengthened bones in limbs
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Gene interaction
the cellular function of numerous gene oviducts contributes to the development of a common phenotype
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what is epigenesis?
development concept whereby each step of development increases the complexity of the sensory organ and is under the control and influence of one or more genes
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sex limited
Autosomal genes whose expression is limited to one sex
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example of sex limited traits
feather plumage in chickens
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Sex influenced
Genes on an autosome that are more readily expressed in one sexF
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example of sex influenced traits
pattern baldnesss in humans. Allele B for baldness acts as dominant in males and recessive in females and appears to be related to the levels of the male sex hormones
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what are temperature sensitive mutations?
expression is affected by the temperature
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what is organelle heredity?
DNA contained in the mitochondria or chloroplasts determine certain phenotypic characteristics of offspring
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what is the maternal effect?
nuclear gene products are stored in the egg and transmitted through the ooplasm to the offspring effecting the genotype
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two forms of extranuclear inheritance
organelle heredity and maternal effect
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what makes the analysis fo inheritance patterns resulting from mutant alleles in chloroplast and mitochondria difficult?
function fo these organelles is dependent on the gene products from the nucleus and the organelle DNA making the origin of mutations affecting the organelle function difficult
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what are the 4 characteristics of cytoplasmic inherited traits?
1-present in male and females,
2-usually inherited from 1 parent, typically the maternal parent.
3-reciprocal crosses give different results
4-exhibit extensive phenotypic variations, even within a single family
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describe how genes are related to chloroplast
genes carried on the DNA encode products involved in photosynthesis and translation and mutation in these genes may inactivate photosynthesis
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products of the maternal genes are
synthesized in the developing egg
stored in the oocyte prior to fertilization
following fertilization, they specify molecular gradients that determine spatial organization within the zygote
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genetic maternal effects
nuclear genotype of the maternal parent
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cytoplasmic inheritance
cytoplasmic genes, which are usually inherited entirely from one parent
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genomic imprinting
genes whose expression is affected by the sex of the transmitting parent
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Dominant
an allele that is always expressed
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recessive
an allele that is masked when the dominant allele is present
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epistasis
A type of gene interaction in which one gene alters the phenotypic effects of another gene that is independently inherited.
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complementary gene interaction
Must have at least one dominant allele at each locus (A-B-) to have the phenotype
